A fuel cell, for example a solid polymer fuel cell, converts chemical energy of a substance directly to electrical energy through an electrochemical reaction produced by supplying reactant gases (a fuel gas containing hydrogen and an oxidant gas containing oxygen) respectively to two electrodes (a fuel electrode and an oxygen electrode) situated in opposition to either side of an electrolyte membrane. One known principal structure for such fuel cells is a so-called stack structure composed of unit cell constituent members each including a membrane-electrode assembly (MEA) of planar shape and of separators, stacked in alternating layers and connected together in the stacking direction.
In the field of such fuel cells of stack structure, there are known a technology which involves integrally molding a seal member at the edges of the unit cell constituent members which are each composed of a membrane-electrode assembly sandwiched from either side by gas diffusion layers. There is another known technology involving integrally molding the separator, the gas diffusion layer, and the seal member. Using these technologies it has been possible, through the agency of seal members, to inhibit leaking of the fuel gas, the oxidant gas, and the cooling medium to the outside from the fuel cell, and to prevent them from mixing.
However, the conventional technologies discussed above cannot be said to afford sufficient ease of assembly and disassembly of the fuel cell stack. For example, where the technology of integrally forming seal members at the edges of unit cell constituent members is employed, during the assembly operation was necessary to alternately stack the separators and the unit cell constituent members; whereas with the technology of integrally forming the separator, the gas diffusion layer, and the seal member, it was necessary to alternately stack the separator-gas diffusion layer assemblies and the MEAs.